System for producing amplitudemodulated pulses



Aug. 30,719,49- w. D. HouGH'roN 2,480,137

SYSTEM Fon PRoDucING AMPLITUE-MQDULATED PuLsExs y' 3 Sheets-Sheet lFiled May 9, 1947 INVENTOR.

0 ,f M W L/ M t Y WW i fvwm/##77124 E 1:: LII u .WJ/I

ma ay MM ATTORNEY W. D. HOUGHTON SYSTEM FOR PRODUGING AMPLITUDE-MODULATDPULSES Filed 'ay 9, 1947 INVENTOR.

ATTORNEY SYSTEM FOR PRODUCING AMPLITUDE-MODULTED PULSES N O T H G U O HD W Filed May 9, '1947K 3 Sheets-Sheet 5 #N0 fwwww www 72/56'5 TMLINVNTOR.

ATTORNEY ltem.

Patented Aug. 30, 1949 SYSTEM Foa PRODUCING AMPIJ'rUDE- MoDULA'rsnrULsEs William D. Houghton, Port Jefferson, N. Y., assignor to RadioCorporation of America, a corporation of Delaware K Application May 9,1947, Serial No. 747,105

21 Claims.

This invention relates to a method of andl means for producing amplitudemodulated pulses of relatively opposite polarities in a'cornmunicationtransmitter system.

More specifically, the invention enables the production of plus andminus amplitude modulated pulses. The pulses generated in the system ofthe invention may have a positive polarity, a negative polarity or be ofzero amplitude, depending upon the amplitude and polarity of themodulating voltage. When the modulating voltage is zero, no pulses aregenerated. When the modulating voltage is maximum and negative, theamplitude of the generated pulse is a maximum in one direction, and whenthe modulating voltage is maximum andpositive, the amplitude of thegenerated pulse is a maximum in an opposite v direction. The variationsin amplitude of the generated pulses are made to be linear with respectto the modulating voltage.

The invention is especially useful in multichannel (multiplex) timedivision systems wherein a common transmission line is sequentiallyassigned to diierent channels each of whichhas its own modulationapplied thereto. The common transmissionlne may feed any suitable radiofrequency generator or transmitter circuit -for modulating the carrierwave, but it is preferred to utilize the amplitude modulated pulses toshift Y the frequency of a frequency modulation transmitter about itsmid-carrier frequency; and since no pulses are produced in the absenceof modulation, full advantage may be taken of the noise limitingqualities of a frequency modulation sys- A more detailed description ofthe invention follows in commotion with a drawing, wherein:

Fig. 1 illustrates, diagrammatically, the transmitting end of amulti-channel pulse communi-k cation system in which the invention maybe employed;

Fig. 2 illustrates the circuit details of a channel unit and the commonoutput equipment embodying the principles of the invention;

Fig. 3 is a series of curves graphically illustrating voltage waveformsat different points of the circuits of Figs. 2, 4 and 5 given inexplanation of the operation of the invention; and

Figs. 4 and 5 show other embodiments 'of the invention. e.

Referringto Fig. 1 in more detail, this gure shows transmittingapparatus for a, plurality of channels each of which is supplied withits own signal modulation. A crystal oscillator A is employed to lock ina pulse oscillator B. The output from pulse oscillator B is coupledthrough lead I to a step voltage wave generator G. The step voltage waveoutput from generator G is coupled through lead ||2 to the inputs of aplurality of channels suitably labeled as channel l units I, 2, 3, etc.Each channel unit produces two simultaneously occurring" pulses whoseamplitudes are differentially modulated in accordance with themodulation applied to that channel. The two pulses from each channelunit are fed to a common channel combining unit |24 which converts thetwo pulses to a-single pulse whose amplitude is modulated plus and minusabout zero or ground potential. The variations in amplitude of thissingle pulse are made linear with respect to the modulating voltage.Channel units l, 2 and 3 are shown diagrammatically connected to thechannel combining equipment |24 over leads IIB, H9 and |20.respectively.- A synchronizing pulse generator D produces asynchronizing pulse of longer duration than the channel output pulsesimmediately after the discharge of the step wave generator G, and iscontrolled by the generator G over lead H3. The combined channel outputpulses from combining equipment |24 plus the synchronizing pulse 'arefed to the common ampliiier |25, which ampllfies the pulse train inpreparation for modulating a radio frequency transmitter T. Thesynchronizing pulse generator D is coupled to the amplifier |25 throughlead H1, while the amplitude modulated channel pulses from the commonchannel combining unit are fed to this same amplifier over lead |30.

The crystal oscillator A produces a. sine wave output whose positive ornegative portion controls the production of a pulse from pulseoscillator B. The oscillator A may be any L. C. or R. C. type dependingupon the stability requirements of the system. .The pulse oscillatorBvmay be a blocking type pulse oscillator which produces D.C. pulses `atthe frequency of the crystal oscillator A. The

time constants of the pulse oscillator B are so chosen that the naturalfrequency of operation of the pulseoscillator is slightly lower than thefrequency of the crystal oscillator.

The step wave generator G produces a stair or step voltage wave havingya plurality of risers of substantially the same amplitude range but ofdifferent voltage values relative to a base line. A condenser in thestep wave generator stores or collects the incremental charges passedthereto by the pulse oscillator, until a predetermined peak or totalvoltage is reached after which it discharges. There are two outputs fromthe step wave generator, one of which is the stair or step voltage waveavailable on lead I I2 and the other of For a more detailed descriptiono! suitable circuits which may be used for the crystal oscillator A,pulse oscillator B and step wave generator G, referenceis made to mycopending application Serial No. 608,957, tiled August 4.1945.

Fig. 2 illustrates the circuit details of a channel unit, it beingunderstood that all channel units are identical except for the biasadjustment. This ligure also illustrates the common channel combiningequipment I 2l which is fed by all channels.

Each channel unit includes a selector vacuumtube 8 which is biased to benormally non-conducting by an adjustable tap 89 on the cathode resistor8. It. will thus be seen that resistor 8 is variable. The step waveoutput from the step wave generatoris ted to the grid of the tube 6 t'.rough a grid current limiting resistor I. Resistor I limits the maximumgrid-to-cathode potential. The tube I is biased so that it becomesconducting on a particular riser yof the applied step voltage wave.yWhen tube 6 becomes conducting, the current in this tube rises i'romzero to a maximum value and remains at`this maximum value i'or'theduration of the applied step wave. AThe condenser 1 in parallel to thecathode resistor 8 servesto bypass A.C. components of cathode current-to ground. The anode of tube 6 is connected through resistor 2 to thepositive terminal B+ of a source oi.' D.C. potential.

It should be understood at this time that the inputs of all selectortubes in the diilerent channels are fed in parallel by the applied stepvoltage wave, and that Athe selector tubes in the different channels aredill'erently biased to become conducting on diflerent risers of theapplied step wave, as a result of which the pulses produced in thediil'erent channels occur sequentially Vat different time intervals.

The anode of selector tube`8 is also coupled to the grid of a normallyconducting vacuum tube 9 through a condenser 5.' The grid of tube 9 isalso connected through a resistor 3 to the terminal B+. The combinationof condenser and resistor 3 forms a diierentiator circuit. The anode oftube 9 is connected to the same B+ terminal through a resistor l, whileits cathode is connected to ground through aresistor I0.

A pair of triode vacuum tubes II and I2 of similar characteristics havetheir cathodes directly connected together and'to the cathode of tube 9,as a result of which resistor I0 is a common cathode resistor for allthree vacuum tubes 9, II and I2. The ilow of current through 'normallyconducting tube 9 produces a voltage drop across resistor I0 which issufficient to bias tubes and I2 below cut-oil. 'I'he value of resistorI0 is so chosen that when tube 9 ceases conducting, the reduction of thebias voltage developed across this resistor enables tubes II and I2 tooperate as` class A amplifiers. For this reason, tube 9 can beconsidered as a gata A source of audio modulation i'or the channel issupplied to the grids oi' tubes I I and I2 in push.. pull or outy-of-phase relation through transformer I3. The anodes of tubes I| and I2are individually connected to the B+ terminal through equal valueresistors Il and I5, respectively, and arev also coupled throughcondensers I6 and 1, respectively, to the grids of vacuum tubes 28 and20.

Tube 20 acts as a class Aampliner and has its anode connected through aresistor I8 to the i condenser I9 to the grid of a triode vacuum tubewhich is the discharge pulse available on lead I I3.

2| also operating as a class A amplifier.

Tube 28 also operates as a class A amplier and has its anode directlyconnected to the anode oi ampliiler tube 2|. Both ampliiers 2| and 28are identical. A common load resistor 29 connects the anodes of the twotubes 2| and 28 to the B+ terminal. The cathodes of tubes 2| and 28 aredirectly connected together, and to ground through a common cathoderesistor 21.

The anodes of tubes 2| and 28 are coupled through a condenser 30 to thegrid of a triode vacuum tube 33 operating as a class A ampliiler. Theanode of tube 33 is connected through a resistor 3| to the B+ terminal,and is also connected through a coupling condenser 32 to the output lead|30 extending to the common ampliiler |25. Plus and minus (positive andnega.- tive) amplitude modulated pulses are derived from the commonchannel combining equipment |24 on lead |30. The manner in which this isaccomplished will now be described more fully.

Tube 6 is biased to be normally non-conducting and is made to startconduction on any desired step riser by adjusting the value of the biasvoltage developed across yvariable cathode resistor 8. When tube 6becomes conducting its anode potential suddenly drops to a low value,causing normally conducting tube 9 to be cutoli. Tube 9 remains cut-oilfor a time determined by the time constants of the differentiatingnetwork 3 and 5. Vacuum tubes II and I2 are normally non-conducting dueto bias vdeveloped across resistor I0 when tube 9 is conducting. The

value of resistor I0 is so chosen that when tube 9 is cut-olf, tubes IIand I2 are biased as class A ampliiiers. Hence, two negative goingpulses (one across resistor I4 and one across resistor I5) are devolepedwhen tube 9 is cut-oil. The duration of these negative pulses is equalto the cut-oil time of tube 9, and is determined by the diierentiatingnetwork 3 and 5. When no modulation is present on the channel, the twopulses are equal in amplitude. When modulation is present on transformerI3, the amplitude of the pulses vary linearly in a push-pull manner.That is, as the pulse across resistor I 4 increases in amplitude, thepulse across resistor I5 decreases in amplitude by an equal amount.

The operation of the common circuit is as follows: The negative pulseacross resistor; I5 is coupled to class A ampliiler 20. The amplicationfactor of 20 is made unity, hence a positive pulse equal in magnitude tothe negative pulse across resistor I5 is developed across resistor I8.Tube 20 can thus be considered a phase inverter tube. The pulsedeveloped across resistor I8 is coupled to the grid of class A amplier2|, while the pulse developed across I4 is coupled to the grid of classA amplier 28.

For the condition where the channel is unvmodulated, the negative pulseacross resistor lI4 ythe pulse across resistor Il. Therefore, since thegrid of tube 2| is driven positive by -the same amount the grid of 28 isdriven negative, there is no voltage change across resistor 29 and nopulse present to drive output tube 33. For the condition wheremodulation is present on transformer I3 and the grid of tube I2 is mademore positive than the grid oi.' tube II. the negative pulse acrossresistor I5 is greater in amplitude than the negative pulse acrossresistor' Il. Hence i the positive pulse on the grid of tube 2| isgreater in amplitude than the negative pulse on the grid of tube 28 anda negative pulse is developed across resistor 23 which results in anegative pulse being applied to the grid of tube 33, and as aconsequence a positive pulse being developed at the oi tube 2| is drivenpositive, and hence a positive pulse is. developed across the grid oftube 33 resulting in a negative pulse being developed comes conductingits anode potential suddenly.

drops to a low value and remains at this value for the remainder of theapplied step voltage wave cycle.

Fig. 3, curve C represents the waveform de veloped across cathoderesistor I0 which is common to tubes 9. II and I2, the dash-dot linelabelled Y indicates the potential below which tubes II and I2 becomeconducting.y The length or duration of these pulses is determined by theR. C. constants of differentiating network 3 and 5 which diierentiatethe negative going edge of the anode voltage wave of tube 6, Fig. 3,curve B.

Fig. 3, curve D shows the Waveform of the modulating voltage applied tothe grid of tube Iii, and Fig. 3, curve E the waveform ofthe modulatingvoltage applied to the grid of tube I2. The waveform of Fig. 3, curveEbears a 130 out-of-phase relationship with that of Fig. 3, curve D. i

Fig. 3, curve F represents the negative going pulses on the anode oftube I2, and Fig. 3, curve G the negative going pulseson the anode oftube ii. tive pulses of Fig. 3, curve F and Fig. 3, curve G are equal inamplitude. This is due to the fact that at the time of conduction oftubes II and I 2, the applied modulating signals are passing throughzero.

Fig. 3, curve H shows the positive pulses at the grid of tube 2i. Thesepulses are equal in amplitude but 180 out-of-phase with those appearingon the anode of tube I2 (Fig. 3, curve F).

Fig. 3, curve I shows the plus and minus pulses as they appear on lead|30 at the output terminal. It vshould bev noted that there are nopulses appearing at times R, S, and T since at these` points the twosine waves Fig. 3d and 3e are at zero amplitude and the positive pulsesin Fig. 3h are equal and opposite to those in Fig. 3g; resulting in theincrease in current in tube 2I being exactly balanced by the decrease incurrent 'in tube 23.

'I'his balance occurs when tubes II and I2 are made conducting at a timewhen the modulating waves applied to their grids have zero amplitude. Atall other times, a' pulse will appear and will It will be seen at timeR, S, and T the negabe either positive or negative. depending upon whichtube (II or I2) carries the greater amount of current when it-is madeconducting. vIn multiplex systems.` the time interval between adjacentlpulses, curves F, G and H oi Fig. 3, contain yall the other channelpulses. -It will ,thus be seen that -the unal output pulses fromeachchannel are either positive or negative in sign and are amplitudemodulated. The

final output pulses from the different channels occur at diierent timeintervals.' For each cycle of operations represented by a singlecomplete step voltage wave, there will be a pulse from each channel unitin the presence of modulating voltage, and this pulse will be eitherpositive or negative, and the pulses from the diilerent f channels occursequentially. In the output of the common ampliiier I25. each cycle ofoperations will also include a synchronizing pulse of longer durationthan the channel pulses and which occurs at the end of the step voltagewave, or after all the channels have each produced one pulse. 'I'hesynchronizing pulse may have an amplitude equal to or 'slightly .greaterthan the maximum amplitude of any channel pulse .under extremes ofmodulation. The synchronizing pulse may be smaller in amplitude if thereceiving equipment is designed to acceptit. Y

Figs. 4 and 5 show other embodiments of the invention which are not asdesirable as Fig. 2 when using a large number of channel units, onaccount of the greater tendency for cross-talk in the systems of Figs.4` and 5, but are desirable for smaller systems due to their simplicity.The same parts which appear in al1 three figures have been given thesame reference characters.

Figs. 4 and 6 employ a transformer 60 in the channel unit for producingthe desired plus and minusfoutput pulses. The operation of Fig. 4 may beunderstood by reference to the curves A to I qi? Fig. 3. Fig. 3 curve Ashows the step voltage wave applied to the grid of selector tube 6. Letit be assumed that the tube 6 of Fig. 4 is so biased as\'to becomeconductive on the second riser of the step waveof Fig. 3, curve A. 'I'hehorizontal dash line p in- Fig. 3, curve A indicates the point ofconduction and the horizontal dash line :r indicates the level at whichthe grid-to-cathode potential of tube 6 reaches zero. The anode.potential of tube 6 is shown in Fig. 3, curve B 'for the conditionassumed above. On the negative going edge vo f the voltage wave 'acrossresistor 2, the normally conducting gate tube 9 is cut-off for a timeinterval determined by the time constants .of diierentiating network 5,3. The negative pulses of the curve C of Fig. 3 indicate the intervalsvduring which tube 9 is cutoE. When tube 3 is cut-oi! the potentialvacross resistor I0 drops, as a result of which tubes II and I2 conductand actas class A ampliiiers during the cut-oil? time of tube 9.

Fig. 3 curves D and E indicate the audio modulation voltage applied tothe grids of tubes II and I2 by transformer I 3. These voltages areidentical but out-of-phase, that is, transformer I3 feeds the grids ofII and I2 in a push-pull manner well known in the art. The waveform F ofFig. 3 represents the negative voltage pulses appearing on one-half ofthe primary winding of transformer B0 due to current in tube I2 whileFig. 3 curve G represents the negative voltage pulses appearing on theother half of the primary winding of 60 due to current in tube II. CurveI of Fig. 3 representsthe plus and minus pulses as they appear acrossthe secondary winding oi transformer 69. are no pulses appearing attimes R, S, and T in Fig. 3, curve I since at these times the modulatingvoltage is passing through zero and the voltage on the grid of tube IIis equal tothe voltage on the grid of tube I2 and hence they carry equalcurrents when conducting and since transformer 60 is a push-pull typethere is no change in voltage across the secondary winding. However, inthe presence of an audio voltage on transformer I3, if thegrid-to-'cathode potential of tube II is made more positive than thegrid-to-cathode potential of tube I2, a pulse is developed across theoutput winding of transformer 60 of a. polarity depending upon theconnections of the transformer. On the next half cycle of the audiovoltage. tube I2 carries more current than tube II and hence a pulse ofopposite polarity is developed across the output winding.

' Fig. 5 shows a modification of the system of Fig. 4 in which push-pulltransformer I3 of Fig. 4 is replaced by a phase inverter tube 49. Theoperation of this circuit follows:

A step voltage wave as shown in curve A of Fig. 3 is coupled to the gridof normally non-conducting tube 6. Tube 6 is biased to become con- Itwill be noted that there ducting on a. particular step riser aspreviously l,

described. When tube 6 becomes conducting its anode potential suddenlydrops to a low value (see curve B of Fig. 3) and remains at this lowvalue for the remainder ofthe step wave cycle. The negative going orfalling edge of the voltage wave on the anode of 6 is differentiated bythe differentiating network consisting of 3 and 5. Thus a negative'pulseis developed on the grid of normally conducting tube 9 sufficient tocause it to cease conducting. Tube 9 remains cut-off for a period oftime determined by the values of 3 and 5.

When-tube 9 is conducting it develops a .voltage across resistor I0suiilcient to maintain tubes II and I2 cut-off. Hence when tube 9 butsoff tubes I I and I2 become conducting. The value of I0 is so ,chosenthat tubes I'I and I2 operate as class A ampliers during the time theyare conducting. .The voltage developed across resistor I0 is as shown inc urve C of Fig. 3. Tube 49 is a conventional phase inverter tube whichproduces a voltage across its plate resistor which is equal to and 180out-of-phase with the voltage developed across its cathode resistor. Thevoltage developed yacross the anode resistor 20 of tube 49 iscoupled tothe grid of tube II via coupling condenser I6 and the voltage developedacross the cathode resistor I8 of tube 49 is coupled to tube I2 viacoupling condenser I1. Elements II4 and I'I5 are the grid leak resistorsfor tubes II and I2 respectively. The modulating signal appearing acrossgrid resistor II4 is shown in curve D of Fig. 3 and the signal appearingacross resistor II 5 is shown in curve E of Fig. 3.

The negative pulse voltage across one-half of the primary of 6D due topulse currents in tube- I2 is shown in curve F of Fig. 3, while thenegative pulse voltage across the other half of the primary of 60 due topulse currents in I I is shown 8 than that on the other and when theybecome conducting (tubes II and I2) a pulse will appear on the output,the polarity being a function of the tube carrying the greater currentand the amplitude being a function of the degree of unbaiance in thegrid voltages.

It will be understood that it is not necessary to employ individualtubes for the triode electrode structures, since if desired, a dual ortwin triode tube can be used which contains two electrode structureswithin a single evacuated envelope.

What is claimed is:

1. In a pulse generating system, the method which includes producing twosimultaneously occurring pulses of the same relative polarity,different'ially modulating said pulses in accordance with a signal, andconverting said two pulses to a single pulse whose amplitude ismodulated plus or minus relative to a reference value.

2. In a pulse generating system, the method which includes producing apair of simultaneously occurring pulses of the same relative polarity,equalizing the amplitudes of said pulses in the absence of modulation,varying the amplitudes of said pulses diilerentially and linearly inaccordance with a modulating signal, and converting said pair ofdifferentially modulated pulses to a singlepulse which has one polaritywhen one pulse of said pair has a larger amplitude than the other, andwhich has an opposite polarity when said'one pulse has a smalleramplitude than the other.

3. In a pulse generating system, the method which includes producingftwosimultaneously occurring pulses of equal amplitude and of the samerelative polarity, modulating the relative amplitudes of said pulses inaccordance with 'a modulating voltage. controlling the ow of spacecurrent vin one path by one of said pulses, controlling the flow ofspace current in another path by the other of said pulses, balancingoutv the effects of the ow of current in said paths when the pulses areof equal amplitude, causing a greater ilow of current in one pathcompared to the other path when said pulses are of different amplitudes,and utilizing said difference in current ow to produce a pulse in onedirection or the other depending upon which path has the greatestcurrent ilow.

4. In a pulse generating system, the method which includes producingfirst and second simultaneously occurring pulses of negative polarityand of equal amplitudes, differentially modulating l the amplitudes ofsaid negative pulses in accordance with a modulating signal, obtaining apositive pulse from, said first negative pulse and of the same relativeamplitude, controlling the flow of space current in one path by saidpositive pulse,

in curve G of Fig. 3. The resulting plus and minus amplitude modulatedpulses are shown in curve I of Fig. 3. I

It should again be noted that when the tubes II and I2 conduct-when themodulating voltage is passing through zero no voltage is developed onthe secondary of 60. This is due to tubes II and I2 carrying equalcurrents. When the voltage on the grid of one tube has a magnitudegreater controlling the flow of space current in another path by saidsecond negative pulse, balancing out the controlling eiects of saidpositive and said second negative pulses, only when said iirst andsecond negative pulses have equal amplitudes,

and utilizing any difference in the controlling effects caused by saiddifferential modulation to produce a pulse whose sense depends uponwhich path carries the greater ilow of current and whose magnitudedepends upon the extent of the dierence in current flow in the twopaths.

5. In a pulse generating system, the method which includes producing apair of simultaneously occurring pulses of the same relative polarity,equalizing the amplitudes of said pulses in the absence of modulation,varying the relative am- 76 plitudes of said pulses linearly Inaccordance with function of the modulating voltage and which has onepolarity when one pulse oi' said pair has a larger amplitude than theother, and which has an opposite polarity when said one pulse has asmaller amplitude than the other.

6. A pulse generating system comprising a ilrst vacuum tube electrodestructure biased to be normally non-conducting, a circuit for supplyinga recurring waveform to said rst structure of a polarity and magnitudeto render it conducting at the frequency of said waveform, a secondvacuum tube electrode'structure biased to be normally conducting, adiflerentiator circuit coupled between the output of said ilrststructure and the input of said second structure, to thereby cause saidsecond structure to cease conducting in re- Y fio' to a single'pulsewhose polarity depends upon which electrode structure oisaid pair passesthe greater amount of current 'and whose magnitude depends upon theextent of difference4 in the amounts of current iiow through bothelectrode structures. A

10. A pulse generating system comprising a pair of vacuum tube electrodestructures, each including a control electrode and an anode. a circuitsponse to the conduction condition of said iirst space paths beingbiased to be non-conducting in the normal conduction condition of saidsecond structure and passing current during the nonconducting conditionof said second structure, means for did'erentially controlling the flowof current in said space paths in accordance with a modulating voltage,and means for deriving vfrom said space pathsa pair of differentiallymodulated pulses having variations in amplitude which' are linear withrespect to the modulating voltage.

7. A pulse generating system comprising a pair of electrode structureseach including an anode and a control element, cathode means for saidstructures, a. bias element in circuit with said cathode means fornormally biasing said electrode structures below cut-oir, individualimpedances in circuit with the anodes of said structures, a circuit forperiodically overcoming the cut-oil bias of said structures to therebyrender them conducting, a modulating circuit coupled to said controlelements in push-pull relation, and means coupled to said impedances forderiving diierentially modulated pulses.

8. A pulse generating system comprising a. pair of electrode structureseach including a cathode, an anode and a grid. a common cathode resistorfor said structures, individual resistors connected between said anodesand the positive terminal of a source of D.C. potential, a circuit forcausing current to ilow periodically through said cathode resistor tothereby periodically cause said electrode structures to conduct, meanscoupled to said grids for supplying a modulating voltage to said gridsin opposing phase relation, and'leads cou'- pled to said individualresistors for deriving therefrom a pair of simultaneously occurringpulses of the same relative polarity but whose amplitudes vary independence upon the modulating voltage.

9. A p'ulse generating system comprising a pair of electrode structureseach including a cathode,

' an anode and a grid, a common cathode resistor tor periodicallycausing said structures to become simultaneously conductive and thennon-conductive, a circuit for supplying a modulating voltage to thecontrol electrodes of said pair of vstructures in out-of-phase relation,and leads coupled to said anodes for deriving from said structures apair of simultaneously occurring pulses of the same relativepolaritywhen said structures simultaneously chan-ge from one currentcondition to the other.

11. AA pulse generating system comprising a pair of vacuum'tubeelectrode structures, each including a, control electrode and anode, acircuit for periodically causing said structures to becomesimultaneously conductive and then non-conductive, a. circuit forsupplying a modulating voltage to the control electrodes of said pair ofstructures in out-.of-phase relation, individual resistors connectedbetween the respective anodes and the positive terminal of a source ofD.C. potential, and means connected to said anodes for derivingtherefrom a pair of simultaneously occurring pulses of negative polaritywhen said structures change from the non-current passing condition tothe current passing condition.

12. A pulse generating system comprising a pair of vacuum tube electrodestructures, each including a control electrode and an anode, a. circuitfor periodically causing said structures to become simultaneouslyconductive and then nonconductive, a circuit for supplying a modulatingvoltage to the control electrodes of said pair of structures inout-of-phase relation, individual resistors connected between therespective anodes V Aand the. positive terminal of a source of D.C.

^ modulating voltage, controlling the flow o! space f l 'current in onepath by one of said pulses, conpotential, a phase inverter amplifiercoupled to "the anode of one of said structures, a second amplifiercoupled to the anode of the other structure, a. third amplifier coupledto the output of said phase inverter, a common load resistor for saidsecond and third ampliers, and means coupled to said common loadresistor for deriving therefrom a pulse whose polarity may be eitherplus or minus depending upon which one of said electrode structurescarries the greater current during the time both electrode structuresare simultaneously conductive.

13. A pulse generating system including means for producing a pair ofsimultaneously occurring pulses of the same polarity whose relativeamplitudes vary linearly in response to a modulating voltage, and means:Ior converting said pair of pulses to a single pulse whose polaritydepends uponwhich one of said pair of pulses has the greater amplitudeand whose amplitude depends upon the extent of difference in amplitudesof said .pair of pulses.

f 14. In a-pulse generating system, the method which includes producingtw simultaneously occurring pulses of equal amplitude and of the samerelative polarity, dinerentially modulating the amplitudes of saidpulses in accordance with a r trolling the ilowof space current inanother path by the other of said pulses, balancing out the effects ofthe iiow of current -in said paths when er ilow of current in one pathcompared -to the other path when said pulses are of diiferentamplitudes, and utilizing said difference in current flow to produce apulse in one direction or the other depending upon which path has thegreatest current iiow, said last means comprising a phase inverteramplifier fed by one of said pulses of said pair, a' second amplifiercoupled to the output of said phase inverter, and a third ampliiler fedby the other pulse of said pair, there being a common load resistor forsaid last two amplifiers, and an output circuit coupled to said commonload resistor.

15. A system for converting a pair of simul taneously occurring pulsesof the same polarity and whose amplitudes vary differentially in ac-4cordance with a modulating voltage to a single pulse, including a phaseinverter amplier fed by one of said pulses of said pair, a secondamplifier coupled to the output ofsaid phase inverter, and

ins a grid, anode and a cathode, a diiferentiator circuit coupledbetween the anode of said rst structure andthe grid of said secondstructure, third and fourth electrode structures each including grid,cathode and anode electrodes, a commoncathode resistor for the cathodesof said second, third and fourth electrode structures, whereby thevoltage developed across said common cathode resistor due to currentflowing in said second structure biases said third and fourth structuresbelow cut-olf, a transformer having a primary winding coupled across theanodes of the third and` fourth structures, and a secondary winding forderiving output pulses from said transformer, and a circuit for applyinga recurring waveform lto the grid of said iirst structure of suchpolarity and magnitude as to cause said first structure to.

conduct, to thereby bias/said secondv structure to the anode-currentcut-oi! condition and cause said third and fourth structures to conduct.

17. A pulse generating system comprising a' first normallynon-conducting electrode struc' ture having a grid, anode and a cathode,a second normally conducting electrode structure having a grid, anodeand a cathode, a differentiator circuit'coupld between the anode of said12 condition and cause said third and fourth tures to conduct, saidcommon cathode resistor having such value that said third and fourthelectrode structures operate as class A amplifiers ture having a grid,anode and a cathode, a second normally conducting electrode'structurehaving a grid, anode and a cathode, a diiferentiator circuit coupledbetween the anode of said first structure and the grid of said secondstructure. third and fourth electrode structures each including grid,cathode and anode electrodes, a common cathode resistor for` thecathodes of said second. third and fourth electrode structures, wherebythe voltage developed across said common cathode resistor due to currentflowing in said second structure biases said third and fourth structuresbelow cut-oil, a transformer having a primary winding coupled across theanodes of the third and fourth structures, and a' secondary winding .forderiving output pulses from said transformer,

and a circuit for'applying a recurring waveform to the grid of saidfirst structure of such polarity and magnitude as to cause said firststructure to conduct, to thereby bias said second structure Ato theanode-current cut-off condition and cause said third and fourthstructures to conduct, said common cathode resistor having such valuethat said third and fourth electrode structures operate as class Aamplifiers wlen said second structure is biased below cut-off, and meansfor applying -a modulating voltage to atleast one of said third andfourth electrode structures.

19. A pulse generating system in accordance with claim 18, characterizedin this, that said last means includes a phase inverter tube. f

20. In a pulse generating and modulating system, the method whichincludes producing two simultaneously occurring pulses of the same rela-Vtive polarity and equal amplitude in the absence of modulation,modulating the amplitudes of first structure and the grid of said secondstructure, third and fourth electrode structures each Y including grid,cathode Iand anode electrodes, a

common cathode resistor'for the cathodes of said second, -third andfourth electrode structures, whereby the voltage developed across saidccmmon cathode resistor due to current iiowing in said second structurebiases said third and fourth structures belowcut-oii. a transformerhaving y a primary winding coupled across the anodes of `7i) Numbersaidpulses relative to each other in accordance with a signal, andconvertininsaid two pulses to a single pulse whose ampli de is modulated`plus or minus relative to a reference value.

conductive,means biasing said structures to operate as class A amplierswhen they become conducting, a circuit for supplying a modulatingvoltage to the control electrode ofatleast one vof said structures, andleads coupled to said anodes for deriving from said structures a pair ofsimultaneously occurring pulses of the same relative polarity when saidstructures simultaneously change from onev current condition to theother.

WILLIAM D. HOUGHTON.

REFERENCES The following references are of record in the ille of thispatent:

, STATES PATENTS Name Date 2,411,062 Schade Nov. l2, 1946 2,415,359

Loughlin Feb. 4, 1947

